A technique for limiting the use period of a product has been proposed so as to perform charging based on a license relating to the use period of the product.
For example, in a technique disclosed in Patent Document 1, when a reproduction instruction for contents is issued, the client receives a server time TT from a server through a network, and stores the received server time TT into a storage module. When the license of the contents to be reproduced has a time limitation, the evaluation of the license is performed based on the stored server time TT, thereby preventing an unauthorized reproduction of contents limited in the reproduction period.